enhzflep - 24-6-2006 at 03:46
Having damaged several sets of digital scales, I find it rather hard to commit another $150 for some accurate to 1/10gm. And am certainly too much off
a cheap-ass to pay $500 for a set accurate to 1/100gm - let alone anything like the ones we used in the chem labs.
After reading the post titled "Amino alcohol via Akabori, trial run" I discovered that rhodium and the hive are active once more.
After a quick scout around the place I happened to come across a link that aroused my interest enormously. "Homemade Microgram Electrobalance"
Somewhat skeptically, I clicked the link, expecting to find a complex piece of equipment that more than made up for the monetary expense saved by the
complexity of the controll circuits and/or microprocessor board and software. Man was I wrong!
The link goes on to detail the construction of a balance that can measure +/- 1% on masses in excess of 1mg ( 0.001g +/- 1% 
) It also claims to have the ability to distinguish mases of as little as 2ug in the
100ug range.
I won't go on, I'll let you all see the marvel of this for yourselves. Just follow the link below. - Accurately weighed chems for synthesis here I
come....... 
Homemade Microgram Electrobalance
12AX7 - 24-6-2006 at 05:24
Hmm seems odd to me to use a 7805 when dealing with milivolts. For something that precise, er, hmm I can't seem to find anything on precision voltage
standards.
Interesting use of a meter to lift things.
Tim
chromium - 24-6-2006 at 05:40
I suppose that this device gives reliable results only if its calibrated before (and after) each important measurement and measurements are repeated
several times.
One can easily take, say, 0.1ml liquid with pipette. Using these scales one can measure what weight is and compute specific gravity of very small
samples. This is great when doing microscale work.
[Edited on 24-6-2006 by chromium]
enhzflep - 24-6-2006 at 16:44
@ 12AX7 - Yeah, that's what I initially thought about the use of the 7805. Then I thought about it some more, and given the low power consumption of
the circuit and the fact that it's powered from 2 x 9v battery, rather than a AC -> DC plug-pack, it seems perfectly reasonable. The two nine-volts
make it a bit expensive, but hey - it is a 'sticky-tape' job.
I especially loved the fact that on the next page, a scale is described that allows automatic measurement and display on a small LCD. Although costing
3 times as much i.e $100 this scale measured the change in weight of a damp 1cm long piece of cotton as the water evaporated.
Pretty impressive I reckon.
jpsmith123 - 24-6-2006 at 18:18
What kinds of syntheses would you be doing at home where you'll be working with tens of milligrams quantities of reactants?
In any case, why bother with something like that (unless you want to build it as a hobby) when you can get what is probably a far more useful (and
rugged) digital electronic scale on ebay for about $25.00 USD (including shipping to anywhere in the world)?
I recently bought one like this, and it works very well.
enhzflep - 24-6-2006 at 18:38
Not really too sure what I'd do that would require milligram accuracy, but to be able to do 1/10ths or grains and fractions thereof would be usefull.
Mostly just to do vastly scaled down synths. I suffer quite a bit from the 'cos-I-can' syndrome.
Bit like a stereo microscope. Don't have any use in mind for one, but I still wouldn't mind having one, you know?
After seeing scales like those you've linked to for so cheap, it does make the whole project seem rather futile admittedly. But it would be mostly for
hobby reasons that I built such a device. (Might not be so fun anymore though 
)
Where I live it would cost closer to $30 US or ~ $40 Aus, but even still, this is chicken feed compared to what I paid for my last 2 sets of 1/10g
scales - $180 and $230 aus for a noname chinese piece-of-shit and for an ohaus unit, respectively.
Thanks jpsmith123.
Sandmeyer - 24-6-2006 at 19:04
I agree with jpsmith123. But - I'd rather get a pocket version 10g/10 mg (for drugs and similar sensitive stuff) and additional one with a 500 g/0.1 g
(for reactions) this last one can be had for under 100 euro from Denver Instruments and even cheaper for second hand of course. Reason for 2 is that
one often wants to weight more than 10 g at a time and even be able to put flasks on a scale for conveniance, it's definetly worth the investment. So
you kind of get a 500 g/10 mg for a very reasonable price, well kind of...
[Edited on 25-6-2006 by Sandmeyer]
Rosco Bodine - 24-6-2006 at 19:44
The Ohaus quad beam 311 is accurate to .01 gram .
No batteries to wear out .
A reloaders grain scale is good too , accurate to .1 grain .
[Edited on 25-6-2006 by Rosco Bodine]
neutrino - 25-6-2006 at 08:19
Hermes gave an excellent discussion of electric vs mechanical scales here. I suggest everyone read it before buying a scale.
I remember this scale being discussed either here or at RS, but I can't find the thread.
cbfull - 25-6-2006 at 17:15
Cole Parmer recently started advertising a digital top-loader that weighs up to 400g, with 0.01 precision for something like $280. Not a bad deal.
I have on older version of this model that only goes to 200g, and it has been great for many years. I rarely have to recalibrate it.